The problem of sensing, e.g. of measuring, high-frequency discontinuous current has been tackled in different ways while taking into account various factors, such as:                cost,        size,        accuracy,        bandwidth,        power losses, and/or        galvanic separation of the measured currents.        
For this purpose it is possible e.g. to resort to a resistive element (such as a shunt), this solution showing however limitations as regards galvanic separation.
Another option is the use of magnetic elements (e.g. Amperometric Transformers, ATs) in combination with sensing resistors.
Such solutions are suitable e.g. for the sensing of high-frequency discontinuous currents, which are typically found in switch mode power supplies.
For example, the current to be sensed may be measured by feeding it into the primary winding of an amperometric transformer, the secondary winding whereof is coupled to a current sensing resistor.
Such a solution may offer a good usage of the magnetic core, together with a large bandwidth and low cost. However, it shows limitations due to the impossibility of sensing the DC component of the current: if a resistor is directly coupled to the secondary circuit, the volt second balance itself makes it impossible to sense the average value of the current to be measured. As a matter of fact, the volt second balance condition brings the average voltage on the sensing resistor to zero.
In a possible development of such a solution, a damping element may be inserted across the terminals of the secondary winding of the amperometric transformer (e.g. an RC network to which the current sensing resistor is coupled via a diode). This solution enables to preserve the DC component; however, a drawback is given by the high magnetic flux generated in the magnetic core, because the diode forward voltage is added to the voltage across the sensing element, when it is “seen” by the amperometric transformer. This may lead to a bigger core size and a higher number of turns.
Moreover the damping circuit, the function whereof is primarily to reset the core during the zero current period, may cause high-frequency noise and/or distortions in the measured current.
Other solutions somewhat akin to such a development are known e.g. from GB 2 378 000 A, US 2003/080723 A1 or DE 37 05 468 A1. For example, the solution proposed in GB 2 378 000 A envisages the generation of a signal proportional to the average current, as measured by a diode which “resets” the amperometric transformer during the period where the current to be measured is zero, thus obtaining a signal proportional to the average current, with large amplitude and therefore a high signal-to-noise ratio.